Electrodynamic loud speaker



Nov. 7, 1933. E. GERLACH ET AL 1,934,184

ELECTRODYNAMIG LOUD SPEAKER Filed Dec. 26, 1931 5/8: jl INVENTORS =3 ERWIN GERLACH HEINZ RL! H BY ATTORNEY Patented Nov. 7, 1933 ELECTRQDYNAMIC LOUD SPEAKER Erwin Gerlach and Heinz Orlich, Berlin-Siemensstadt, Germany, assignors to Siemens &' Halske, Aktiengeseilschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application December 26, 1931, Serial No. 583,297, and in Germany September 16, 1930 8 claims; (01. 179-1155) The invention is concerned with a horn type electrodynamic loud speaker which distinguishes itself by an extremely good reproduction of the highest and the lowest pitches with satisfactory efiiciency. I v

Horn loud speakers based upon the electrodynamic drive principle are fundamentally known in the art. These known loudspeaker constructions generally comprise a circular, calotteshaped or conical diaphragm with a circular oscillation coil. Other known embodiments are loud speakers with four pole magnet systems. In

the systems known in the prior art, however,

only about onehalf of the active wire length is utilized, with a resultant poor efficiency of the arrangement. The magnet system inthis case is adapted to the form'of a coil, just as in the known loud speakers with square coils whose magnet system consists of a square middle pole and two pole shoes which are disposed upon two opposite sides of the central pole.

In order to insure faithful reproduction and a high efiiciency it is imperative to make the oscillating system as light in weight as feasible and to raise the field intensity of the air-gap to a maximum value. However, the lightness of the diaphragm should not be driven to a point where rigidity is impairedas a consequence. In fact, up to the highest frequencies, generally up to 3,000 cycles, the diaphragm should oscillate en bloc or piston fashion (as a rigid whole) ,and this is possible only if the diaphragm is of maximum stiffness.

In the case of diaphragms of circulancalotte and cone-shape, an increase in rigidity-is insured with the sacrifice of lightness or an increase in volume or mass. But this fact, in turn, impairs the reproduction particularly of the high frequencies. v r l Now, the present invention is predicated upon a recognition and understanding of the fact that an improvement of electrodynamic loudspeakers is feasible by a departure from, or abandonment of, the customary circular form of the diaphragm with a circular coil. Hence, according td th invention an angular, preferably a rectangular form of diaphragm is used in combination with a square coil. To be more precise, it has been found to be most advantageous tomake the diaphragm and the coil in theform of an elongated rectangle .and to dispose the driving coil at the margin of the diaphragm so that a box likestruc- .ture is obtained the bottom of which consists of be kept far lower than in the case of, a circular the diaphragm while the sides thereof are the sides of the coil.

Now the said form of construction offers a number of essential technical advantages. Known v pot-type magnets are usually found in electro- 69 dynamic loud speakers with circular oscillation coil involve much leakage or'dispersion so that owing to the high field intensity desirable to secure highefliciency, the utilization of the aggregated magnetic fiux that is set upis greatly dimin .ished. Another point is that the Joule heat dissipated by the energizing current of the field coil can not be readily carried away owing tothe fact that the coil is built into the pot magnet with the result that thecurrent density in the energizingcoil, and thus the effective ampere turns, are able to assume only low values. However, the novel arrangement here disclosed provides improvements not only with reference to the magnet system, but also respecting the oscillating system of the. loudspeaker.

' In'the preferably elongated and rectangular form of the diaphragm according to the invention, two natural periods arise. They are, namely, one natural period in longitudinal sense and another one in transversal direction. The former does not make itself unfavorably felt because of the cophasicdrive of the diaphragm so that the diaphragm can be made any desired length. Also the load capacity may thus also be raised at will in contradistinction towhat is true to diaphragi'ns known in the earlier art-where an increase in surface occasions a reduction in the natural period whereby reproduction owing tothe occurrence of the resonance peak is substantially reduced. 1

The width of the diaphragm may be readily chosen so that the transversal vibration of the diaphragm can be shifted to. a very high point, in fact. close to the limit of the frequency range or band preferably or predominantly to be re produced. The transversal vibration may also be vshifted by means of reinforcement ribs or ins and corrugations as is well known in the art. The weight of the diaphragm in this manner may diaphragm possessing identical acoustic properties. According to the present invention it has been feasibleto develop systems in which, in the presenceof a transversal natural vibration of about 6,000 cycles, 1, e., a diaphragm of great rigidity the oscillating system (diaphragm; and

conductor) involved a weight of less than 0.08

gram per square centimeter of ,eiiective surface. The diaphragm may be considered, compared toll) the transformation space, as an air tight diaphragm since a pressure transformation of a ratio of at least 1:10 is provided for the purpose of increasing the efiiciency. This is the ideal oscillating diaphragm to be striven for. The marginal drive prevents the arising of partial vibrations in the diaphragm. The leverage between the driving force and the supporting means is nearly of zero value due to the fact that the driving force acts upon the diaphragm in the neighborhood of the diaphragm supporting means. As a result the diaphragm is able to respond en bloc (piston fashion) to the motions of the coil.

In addition to these acoustic advantages the new loud speaker here disclosed offers substan-- tial advantages also in manufacturing respect. Simple straight ground magnet pieces may be used for the constructure of the magnet system. The magnet system may also consist of a-U -shaped piece having the preferably rectangular and elongated middle pole disposed inthe middle thereof. Preferably, pole plates are placed upon the lateral limbs. If desired the plates may be connected by means of screws and slots with the lateral limbs in order to allow for an adjustment of the air gap between the pole plate and'the center pole. The shape of the elongated rectangle for the center pole, inter alia, oifers the advantage that the dynamically acting transverse sides of the oscillation coils corresponding in shape to the form of the middle pole, may be chosen very short in reference'to the aggregate conductor length.

As previously pointed out the diaphragm is furnished with transversal fins or. ribs in order that the transversal vibrations may be shiitedas high as possible. If this diaphragm is fitted into the mouth of the horn or funnel, then the compression space is unnecessarily enlarged by the space between the reinforcing ribs or fins or corrugations, and the efficiency of the entire arrangement is diminished. I-Iencawhile the diaphragm is provided with fins or corrugations forming reinforcing means, the acoustically active surface is smoothed by covering the surface of the diaphragm with tissue paper, ordinary paper, thin metal foil or some other layerof suitable substance so that the-compression space is correctly pre-calculable and may be chosen and fixed at the optimum value from a technical viewpoint. The covering layer is somewhat'wider than the width of the diaphragm so that strips protrudeat the longitudinaledges' of the diaphragm, these strips being adapted to be fixed to the outer poles. The covering surface inthis manner also serves to support the diaphragm. Owing to the cophasic drive of the entirediaphra'gm, and because of the fact that the distance from the end of the diaphragm to the mouth of the horn is greater than the distance between the -middle of the: diaphragm to the horn mouth, the pressure transformation-is liable to involve a marked diminution or attenuation of certain frequency ranges or bands; This is avoided by arranging the-compression space so that it is not in direct connection with or adjacent to the mouth of the funnel or horn. In fact, it

'is connected with the horn through channels or slots in such a fashion that the acoustic waves reaching the mouth of the horn after having been radiated off from the diaphragm, are substantially of the same phase. g

i The air space between the diaphragm and the central pole should be in communication later.-

ally or through the middle pole, with the outside air to prevent damping. According to a still further object of the invention this is insured by arrangingthe conductor carrying the voice or audiofrequency currents so that a little air gap is produced between the diaphragms and the coil side at the narrow ends of the diaphragm. The conductor is attached to the longitudinal sidesof the diaphragm by being clamped around strips of Pertinax or the like which are connected'along their edges to the diaphragm. The strips also serve as reinforcements for the diap as The invention is illustrated by the accompanying drawing in which,

Fig. 1 is an isometric view showing the magnet system and the field winding,

Fig; 2-is an isometric view showing an approved iorm ofthe assembled diaphragm,

Fig. 3 is an isometric view showing a diaphragm having a modified form of driving conductor,

Fig. 4 is a cross sectional view showingthe assembled driving unit; I Fig. 5 is an enlarged view of a portion of Fig. 4, and

Fig. 6 is a, side view of the assembled appara- The system 1 preferably made in one piece and plates 2 as well as the center pole plate 3. The pole plates are adjustably secured to the poles by means of screws passing through slots in the pole plates. The interiorly disposed field coil 4 is readily able to give oil dissipated heat on its transversal faces inasmuch as the same is in contact with the outside air, in contradistinction with the usual forms of construction of electrodynamic loud speakers where the magnet coil is located inside the pot. Abduction'of heat is furthermore promoted by the aid of sheets or lamina: 5 consisting of material possessing high heat conducting powers, which are inserted in the field coil. I t

Fig. 2 shows the oscillation coil 6 with the diaiio phragm 7 (not shown in Fig. l) The diaphragm phragm. The attachment is preferably obtained by-means of pasting.-

i Fig. 3 shows the diaphragm and the .system without the surface 8. The Pertinax strips 9, the conductor 10 pressed around the same. (which corresponds to the oscillation coil in Fig.2) as well as the reinforcement of the-diaphragm .consisting of corrugations 7a, can be clearly seen.

iio

The corrugations are equivalent. to T-shaped reinforcements. V

Figl 4 shows, partly in section, an embodiment of the novel loud speaker which differs from the embodiment shownin Figs. 1-3, as regards the mode of securing or attaching the diaphragm.

The U-magnet system 11 with the central pole 12 and the outer pole plates 13, surroundsthe exciter coil 14. The coil 14 is carrying the speech or audiofrequency currents projects into the' air gap between thefcentral pole-12 and the pole plates 13.- The'coil 14' consisting of a single turn,

is made of a, wire 15 which is pressed around the Pertinax strips 16. The strips 16 are secured to the longitudinal sides of the diaphragm 17. The diaphragm 17 is fastened to a piece of silk material 18 which extends over a frame 19. The said frame 19 is secured to the plates 13.

Centering of the oscillation coil in the air gap is not attended with any difliculties. If the holes provided in the flange are placed co-axially with the holes in the pole plates, the coil is able to move inside the air gap. A spacer frame 21 consisting of hard paper or sheet metal material is placed between the frame 19 which is screwed fast on the outer pole plates 13, and the flange 20. The pressure transformation space 22 is easily adjustable in this manner. The flange 20 is connected through the long equal length tubes 23 as shown in Fig. 6, with the attaching piece 24 which is adjacent to the mouth of the horn.

What we claim is:

l. A vibratile system for an electrodynamic acoustic device comprising a pair of conductors and an elongated box-like structure open at its bottom and at its two shorter ends, the top of said structure constituting a sound wave producing portion, and the longer sides of said structure constituting supports for said conductors, said sides and said conductors constituting the driving portion of said vibratile system.

2. A vibratile system for an acoustic device of the electrodynamic type comprising an elongated rectangularly shaped sound wave producing portion, reinforcing means for said sound wave producing portion consisting of corrugations extending transversely of said sound wave producing portion, and a driving portion consisting of strips of hard paper connected along their edges substantially to the longitudinal edges of-the sound wave producing portion, and a conductor pressed around said strips of hard paper.

3. A vibratile system for an acoustic device of the electro-dynamic type comprising a sound Wave producing portion, a driving portion, reinforcing means for said sound wave producing portion comprising corrugations extending at right angles to the direction of motion of said driving portion, and a layer of silk covering the corrugations in said sound wave producing portion and extending beyond the limits of said sound wave producing portion to provide means for fastening the vibratile system to the outer pole pieces of the magnet system.

4. A magnet system for an electro-dynamic acoustic device comprising an elongated magnet which is substantially E-shaped in cross section, a winding surrounding the middle limb of said magnet arranged so that it is exposed to the outer air at the ends of said magnet, cooling fins imbedded in said winding and extending from the ends thereof'into the open air, and pole plates secured to each of the limbs of said magnet and arranged to provide a pair of elongated air gaps.

5. A magnet for an electro-dynamic acoustic device comprising an elongated magnet system which is substantially E-shaped in cross section, a winding surrounding the middle limb of said magnet system arranged so that it is exposed to the outer air at the ends of said system, pole plates secured to each of the limbs of said magnet system and arranged to provide a pair of elongated air gaps, and laminae of material having high heat conducting properties inserted in said coil and extending outwardly therefrom into the open air whereby heat from said coil is readily dissipated.

6. A loud speaker of the electro-dynamic type comprising a magnet system for providing an electro-magnetic field, a diaphra m. said diaphragm consisting of a conductor portion adapted to cooperate with said magnetic field and an elongated rectangularly shaped sound wave producing portion, means providing a compression space above saidsound'wave producing portion, and channels for connecting said compression space with an acoustic horn.

'7. A loud speaker of the electro-dynamic type comprising a magnet system for providing an electro-magnetic field, a diaphragm, said diaphragm consisting of a conductor portion adapted to cooperate with said magnetic field and an elongated rectangularly shaped sound 'wave producing portion, means providing a compression space above said sound wave producing portion and channels for connecting said compression space with an acoustic horn, said channels consisting of a plurality of tubes of equal length extending between a common aperture at the smaller opening of said horn and different points along said elongated diaphragm.

8. An acoustic device of the electro-dynamic type comprising means providing a magnetic field, a diaphragm consisting of a portion for cooperating with said magnetic field and a sound wave producing portion, said sound wave producing portion having an elongated rectangular shape, a layer of silk covering said sound wave producing portion and extending there beyond, a frame to which is secured the portion of said layer of silk extending beyond said sound wave producing portion, and means for fastening said frame to' said magnet system.

ERWIN GERLACH. HEIl-VZ ORI ICH. 

